Abstract
Nearly two decades ago, Alexei Kitaev proposed a model for spin- particles with bond-directional interactions on a two-dimensional honeycomb lattice which had the potential to host a quantum spin-liquid ground state. This work initiated numerous investigations to design and synthesize materials that would physically realize the Kitaev Hamiltonian. The first generation of such materials, such as NaIrO, -LiIrO, and -RuCl, revealed the presence of non-Kitaev interactions such as the Heisenberg and off-diagonal exchange. Both physical pressure and chemical doping were used to tune the relative strength of the Kitaev and competing interactions; however, little progress was made towards achieving a purely Kitaev system. Here, we review the recent breakthrough in modifying Kitaev magnets via topochemical methods that has led to the second generation of Kitaev materials. We show how structural modifications due to the topotactic exchange reactions can alter the magnetic interactions in favor of a quantum spin-liquid phase.
Highlights
4d/5d honeycomb layered materials have been vigorously studied due to their potential in realizing a quantum spin-liquid (QSL) ground state [1,2,3,4,5,6,7,8]
First introduced by Alexei Kitaev in 2006, the Kitaev model is an exactly solvable theoretical model with bond-dependent Ising interactions among spin-1/2 degrees of freedom on a two-dimensional (2D) honeycomb lattice, which is described by the Kitaev Hamiltonian: H = − ∑ KγSiγSjγ [9]
The applications of a Kitaev QSL in quantum information and the possibility of realizing Majorana fermions have inspired numerous investigations into quasi-2D honeycomb materials [1,3,10,11,12]. Such materials are colloquially labelled Kitaev magnets as they support a sizable Kitaev interaction; one needs to consider that other interactions such as Heisenberg exchange are present and compete with the Kitaev interaction in the so-called Kitaev magnets [3,10]
Summary
4d/5d honeycomb layered materials have been vigorously studied due to their potential in realizing a quantum spin-liquid (QSL) ground state [1,2,3,4,5,6,7,8]. The applications of a Kitaev QSL in quantum information and the possibility of realizing Majorana fermions have inspired numerous investigations into quasi-2D honeycomb materials [1,3,10,11,12]. The first generation of Kitaev magnets, namely Na2IrO3, α-Li2IrO3, Li2RhO3, and α-RuCl3, were synthesized using conventional solid-state methods at high temperatures (T > 700 ◦C). In these materials, heavy transition metal ions (Ru3+, Rh4+, and Ir4+) are octahedrally coordinated with oxygen or chlorine atoms (Figure 1a), and the edge-sharing octahedra create honeycomb layers (Figure 1b). We will first explain the different types of exchange reactions (partial and complete), discuss the interplay between topochemical reactions and magnetism, and present heat capacity and magnetization data to compare the properties of the first- and second-generation Kitaev magnets
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